This invention relates to a process for producing polyether-containing compounds. More specifically, it pertains to a process of neutralizing alkaline catalysts used in the production of polyether polyols, and to polyols produced by said process.
Polyether polyols prepared from alkylene oxides have been utilized in lubricants, emulsifiers, plasticizers, solvents, and as intermediates in the preparation of polyurethane and polyurethane-modified polyisocyanurate foams.
The production of a polyether polyol from alkylene oxides is ordinarily carried out by the addition of the alkylene oxides to an initiator compound in the presence of an alkaline catalyst at temperatures of from about 70.degree. C. to about 160.degree. C. The alkaline catalyst is usually present in quantities of about 0.05 percent to about 1 percent by weight of the reactants. A typical production method involves the reaction of propylene oxide with propylene glycol in the presence of potassium hydroxide. The resulting crude polyol contains potassium hydroxide. The potassium hydroxide is typically removed so that the polyol will not react erratically with an isocyanate in polyurethane production.
Various methods have been utilized to reduce the level of residual alkaline materials in the final polyol product. Among these methods are included the neutralization of the alkaline materials with hydrochloric acid followed by separation of precipitated alkali metal salts and removal of excess acid. This method is described in U.S. Pat. No. 3,016,404. For some applications, the neutralization method employing hydrochloric acid was an improvement over neutralization methods employing sulfuric acid, phosphoric acid, carbon dioxide, and the like. The hydrochloric acid method is advantageous in that effective neutralization occurs rapidly and excess acid can be removed by gas stripping means. The hydrochloric acid method is disadvantageous in that hydrochloric acid is toxic and corrosive. This method has another important disadvantage. Since determination of the exact amount of acid necessary to neutralize the residual catalyst is extremely difficult, an excess of acid is conventionally used. Thus, excess acid must be readily removable from the polyether polyol, because if excess acid remains in the final polyol product, the presence of said acid may lead to undesirable consequences. For example, excess acid may tend to degrade the polyether chains and may adversely affect materials, such as surfactants and alkaline catalysts, which are typically added to the polyol in the preparation of polyol master batch formulations.
Another method for effectively neutralizing the residual alkaline materials and removal of same involves the use of solid organic acids. This method is described in U.S. Pat. No. 3,000,963. Solid organic acids such as oxalic, benzoic, citric, succinic, fumaric, phthalic, and the like were utilized to neutralize the residual alkaline materials in the crude polyether polyol. Excess acid and the precipitated alkali metal salt were subsequently removed by filtration. One of the requirements of the solid organic acid utilized in this method is that the organic acid, and the salt of the acid and the alkaline catalyst, be insoluble in the polyether polyol.
The use of an excess of formic acid to neutralize an alkali metal hydroxide catalyst in a crude lower alkylene oxide-polyhydroxy initiator adduct is described in U.S. Pat. No. 3,299,151. Said patent teaches the use of an amount of formic acid sufficient to precipitate substantially all of said catalyst, and requires the subsequent removal of the precipitate in order to obtain a polyol which would be suitable for use in the production of flexible polyurethane foams. The excess acid was removed by stripping means.
The use of oleic acid, either alone or in combination with certain sulfonic acids, to neutralize basic catalysts in polyols prepared using polyhydric alcohol initiators is described in U.S. Pat. No. 4,110,268. The resulting salt is not removed from the polyol, and the salt acts as a strong catalyst for the reaction in which the polyol is typically employed. A polyol having a high degree of inherent catalytic activity due to such a salt is undesirable for use in many applications. For example, intricate molds may be employed in the preparation of detailed parts from polyurethane and polyurethane-modified polyisocyanurate foams. The use of such molds makes it desirable to employ a polyol/polyisocyanate mixture which has a relatively long foam time so that the mold may be completely filled before the mixture sets up as a foam. Clearly, it would be undesirable to employ a polyol having a high degree of inherent catalytic activity in such an application.
In view of the disadvantages of the methods of the prior art, it would be desirable in the production of polyols to have an efficient and inexpensive method of neutralizing alkaline catalysts, which would not produce solid precipitates, which would not employ a toxic and corrosive neutralizing agent such as hydrochloric acid, and which would not produce a polyol having a high degree of inherent catalytic activity.